1. Field of the Invention
This invention generally relates to network communication systems, and more particularly to systems operating on wired media such as powerline and phoneline, that permit shared channel access to other transmitters.
2. Description of the Related Art
Existing methods for reliability, in systems with large packet duration relative to the transmission delay, typically include the immediate repeating of a packet not received. In a system with random noise, where the probability of a packet failure is independent of previous packets results, this is a reasonable procedure. In systems with a dedicated channel, it is also reasonable to repeat the transmission of the same packet until it is successfully received, since attempting to transmit a different packet on the same path will have no better chance of success than the current packet.
There are systems where several transmitters contend for a single channel in the environment of bursty channel noise. For such a system, attempting an immediate retransmission, or even backing off for a short period of time, may not improve the chances of a successful transmission. Retransmissions attempted during a long burst of noise are as likely to fail as the initial transmission, wasting precious channel capacity. However, different transmitter/receiver pairs may not necessarily encounter the same noise burst, and some of these pairs may have a better chance of communicating a packet through than the pair that has just experienced a packet failure. Some existing carrier sense multiple access with collision avoidance (CSMA/CA) systems do delay transmissions as part of a random backoff procedure due to packet failure, assuming that the failure is due to a collision, where a collision is the simultaneous transmission by two or more devices. However, in systems where the noise bursts are long relative to the packet duration, this type of backoff procedure doesn't adequately address the problem.
In other conventional systems where the packet duration is small relative to the transmission delays (e.g., satellite communication systems), multiple packets can be sent before the transmitter receives an acknowledgement that the first packet has been received. Hence, these systems incorporate an inherent delay, which incidentally improves the reliability of any repeated transmission in bursty environments. However, in systems where the packet duration is large relative to the transmission delays, and the acknowledgement is coupled with the transmitted packet, the repeated transmission occurs immediately after the failed packet and prior to transmission of the next packet. In a bursty environment, this immediate repeat likely wastes channel capacity. Some existing CSMA/CA systems do delay transmissions as part of a random backoff procedure due to packet failure, based upon the presumption of a simultaneous transmission collision, but these systems do not distinguish between a collision with another packet and noise bursts. Prior to the advent of powerline networks, bursty channels have tended to be more prevalent in wireless packet networks. However, wireless packet networks have addressed this problem with other techniques, such as frequency hopping or wideband coding.
It would be advantageous if a system existed that permitted a transmitter to make a determination of whether its transmissions were failing due to a long burst of noise in the channel.
It would be advantageous if the above-mentioned transmitter could release the channel for use by other transmitters when it determines that a long burst of noise is present.
It would be advantageous if the above-mentioned transmitter could calculate a retransmission schedule to efficiently complete its transmission in the presence of a long burst of noise.